As part of an agreement to serve Pepsi products in its restaurants, fast food chain Arby’s is obligated to feature the soda in at least two television advertisements every year. But this year, Arby’s forgot.

As the company focused on a relaunch around a new tag-line, “We have the meats,” the contract with Pepsi simply slipped everybody’s minds, according to Rob Lynch, chief marketing officer and brand president of Arby’s. Mr. Lynch says the company’s 2014 TV spots have been more focused on that meaty message as opposed to more conventional spots that promote menu items — standard ads where a tall glass of Pepsi fits easily next to a sandwich.

In early October, Pepsi reached out to Arby’s with a friendly reminder: You need to include us in one more ad this year. The problem was that Arby’s already had its end-of-the-year creative ready to go — and it didn’t include Pepsi.

So Mr. Lynch had to go back to the team at Fallon, a Minneapolis-based ad firm owned by Publicis that handles creative for Arby’s.

“Their ads are kind of like their babies. To go in after we shot them and shoehorn something in is like the worst client move you could ever make,” Mr. Lynch said.

But Fallon, following a directive from Mr. Lynch to try to “make him uncomfortable,” sent back an ad poking fun at the Arby’s mix-up: a full pint of Pepsi screens for 30 seconds as the thunderous voice of Ving Rhames describes the corporate faux pas. It finishes with the tag-line, “Arby’s. We have Pepsi.”

Mr. Lynch said the ad had him hysterically laughing, so he ran it by Pepsi, and they agreed. The spot will run from Dec. 7 to Dec. 13 in the Minneapolis, New York, and Los Angeles markets.

“We applaud Arby’s unconventional approach to marketing and when they came to us with this idea, we thought it would be a fun, creative way to highlight our partnership,” Roberto Rios, chief marketing officer for PepsiCo’s food service division, said in an emailed statement.